Database Variable Size Entry Container Page Reorganization Handling Based on Use Patterns

ABSTRACT

A page is loaded into memory of an in-memory database system. Thereafter, it is determined whether to reorganized the page based on how such page is used. Based on such determination, the page is either reorganized by filling any free space gaps in memory and then, use of the reorganized page is enabled or, otherwise, use of the page is enabled without reorganization.

TECHNICAL FIELD

The subject matter described herein relates to enhanced techniques forhandling reorganization of pages having variable entry sizes loaded intomemory of an in-memory database system.

BACKGROUND

In-memory databases are database management systems that rely on mainmemory for computer data storage. With such databases, pages are loadedinto memory which provide for more rapid and efficient access to dataencapsulated within such pages. As these pages are modified, entries canbe added or deleted which can result in gaps within such pages.

SUMMARY

In one aspect, a page is loaded into memory of an in-memory databasesystem. Thereafter, it is determined whether to reorganized the pagebased on how such page is used. Based on such determination, the page iseither reorganized by filling any free space gaps in memory and then,use of the reorganized page is enabled or, otherwise, use of the page isenabled without reorganization.

The determining can include measuring a number of different entry sizesused by the page.

The determining can include measuring an amount of fragmentation withinthe page. Further, the determining can be based on whether there areuniform entry sizes in the page. In addition or in the alternative, thedetermining can be based on whether the page is configured such that newentries are added and oldest entries are deleted when space is needed.

Information about the page can be stored in a transient data structurein a persistence layer of the in-memory database system identifying freespace within the page and deleted entries within the page that can bereused.

The page can be one of a plurality of pages forming a page chain. Thepage chain can be encapsulated within a variable size entry datacontainer.

The reorganizing can cause the page to have a first portion with entriesand a second, different portion, of contiguous free space.

Non-transitory computer program products (i.e., physically embodiedcomputer program products) are also described that store instructions,which when executed by one or more data processors of one or morecomputing systems, cause at least one data processor to performoperations herein. Similarly, computer systems are also described thatmay include one or more data processors and memory coupled to the one ormore data processors. The memory may temporarily or permanently storeinstructions that cause at least one processor to perform one or more ofthe operations described herein. In addition, methods can be implementedby one or more data processors either within a single computing systemor distributed among two or more computing systems. Such computingsystems can be connected and can exchange data and/or commands or otherinstructions or the like via one or more connections, including but notlimited to a connection over a network (e.g., the Internet, a wirelesswide area network, a local area network, a wide area network, a wirednetwork, or the like), via a direct connection between one or more ofthe multiple computing systems, etc.

The subject matter described herein provides many technical advantages.For example, the current subject matter provides for quicker and moreefficient (processor-wise) allocation of entries into pages loaded intomemory of an in-memory database system.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a system diagram illustrating an example database system foruse in connection with the current subject matter;

FIG. 2 is a system diagram illustrating an example database system thatcan support distribution of server components across multiple hosts forscalability and/or availability purposes for use in connection with thecurrent subject matter;

FIG. 3 is a diagram illustrating an architecture for an index server foruse in connection with the current subject matter; and

FIG. 4 is a process flow diagram illustrating page reorganizationhandling for pages having variable sized entries.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a diagram 100 illustrating a database system 105 that can beused to implement aspects of the current subject matter. The databasesystem 105 can, for example, be an in-memory database in which allrelevant data is kept in main memory so that read operations can beexecuted without disk I/O and in which disk storage is required to makeany changes durables. The database system 105 can include a plurality ofservers including, for example, one or more of an index server 110, aname server 115, and/or an application server 120. The database system105 can also include one or more of an extended store server 125, adatabase deployment infrastructure (DDI) server 130, a data provisioningserver 135, and/or a streaming cluster 140. The database system 105 canbe accessed by a plurality of remote clients 145, 150 via differentprotocols such as SQL/MDX (by way of the index server 110) and/orweb-based protocols such as HTTP (by way of the application server 120).

The index server 110 can contain in-memory data stores and engines forprocessing data. The index server 110 can also be accessed by remotetools (via, for example, SQL queries), that can provide variousdevelopment environment and administration tools. Additional detailsregarding an example implementation of the index server 110 is describedand illustrated in connection with diagram 300 of FIG. 3.

The name server 115 can own information about the topology of thedatabase system 105. In a distributed database system, the name server115 can know where various components are running and which data islocated on which server. In a database system 105 with multiple databasecontainers, the name server 115 can have information about existingdatabase containers and it can also hosts the system database. Forexample, the name server 115 can manage the information about existingtenant databases. Unlike a name server 115 in a single-container system,the name server 115 in a database system 105 having multiple databasecontainers does not store topology information such as the location oftables in a distributed database. In a multi-container database system105 such database-level topology information can be stored as part ofthe catalogs of the tenant databases.

The application server 120 can enable native web applications used byone or more remote clients 150 accessing the database system 105 via aweb protocol such as HTTP. The application server 120 can allowdevelopers to write and run various database applications without theneed to run an additional application server. The application server 120can also used to run web-based tools 155 for administration, life-cyclemanagement and development. Other administration and development tools160 can directly access the index server 110 for, example, via SQL andother protocols.

The extended store server 125 can be part of a dynamic tiering optionthat can include a high-performance disk-based column store for very bigdata up to the petabyte range and beyond. Less frequently accessed data(for which is it non-optimal to maintain in main memory of the indexserver 110) can be put into the extended store server 125. The dynamictiering of the extended store server 125 allows for hosting of verylarge databases with a reduced cost of ownership as compared toconventional arrangements.

The DDI server 130 can be a separate server process that is part of adatabase deployment infrastructure (DDI). The DDI can be a layer of thedatabase system 105 that simplifies the deployment of database objectsusing declarative design time artifacts. DDI can ensure a consistentdeployment, for example by guaranteeing that multiple objects aredeployed in the right sequence based on dependencies, and byimplementing a transactional all-or-nothing deployment.

The data provisioning server 135 can provide enterprise informationmanagement and enable capabilities such as data provisioning in realtime and batch mode, real-time data transformations, data qualityfunctions, adapters for various types of remote sources, and an adapterSDK for developing additional adapters.

The streaming cluster 140 allows for various types of data streams(i.e., data feeds, etc.) to be utilized by the database system 105. Thestreaming cluster 140 allows for both consumption of data streams andfor complex event processing.

FIG. 2 is a diagram 200 illustrating a variation of the database system105 that can support distribution of server components across multiplehosts for scalability and/or availability purposes. This database system105 can, for example, be identified by a single system ID (SID) and itis perceived as one unit from the perspective of an administrator, whocan install, update, start up, shut down, or backup the system as awhole. The different components of the database system 105 can share thesame metadata, and requests from client applications 230 can betransparently dispatched to different servers 110 ₁₋₃, 120 ₁₋₃, in thesystem, if required.

As is illustrated in FIG. 2, the distributed database system 105 can beinstalled on more than one host 210 ₁₋₃. Each host 210 ₁₋₃ is a machinethat can comprise at least one data processor (e.g., a CPU, etc.),memory, storage, a network interface, and an operation system and whichexecutes part of the database system 105. Each host 210 ₁₋₃ can executea database instance 220 ₁₋₃ which comprises the set of components of thedistributed database system 105 that are installed on one host 210 ₁₋₃.FIG. 2 shows a distributed system with three hosts, which each run aname server 110 ₁₋₃, index server 120 ₁₋₃, and so on (other componentsare omitted to simplify the illustration).

FIG. 3 is a diagram 300 illustrating an architecture for the indexserver 110 (which can, as indicated above, be one of many instances). Aconnection and session management component 302 can create and managesessions and connections for the client applications 150. For eachsession, a set of parameters can be maintained such as, for example,auto commit settings or the current transaction isolation level.

Requests from the client applications 150 can be processed and executedby way of a request processing and execution control component 310. Thedatabase system 105 offers rich programming capabilities for runningapplication-specific calculations inside the database system. Inaddition to SQL, MDX, and WIPE, the database system 105 can providedifferent programming languages for different use cases. SQLScript canbe used to write database procedures and user defined functions that canbe used in SQL statements. The L language is an imperative language,which can be used to implement operator logic that can be called bySQLScript procedures and for writing user-defined functions.

Once a session is established, client applications 150 typically use SQLstatements to communicate with the index server 110 which can be handledby a SQL processor 312 within the request processing and executioncontrol component 310. Analytical applications can use themultidimensional query language MDX (MultiDimensional eXpressions) viaan MDX processor 322. For graph data, applications can use GEM (GraphQuery and Manipulation) via a GEM processor 316, a graph query andmanipulation language. SQL statements and MDX queries can be sent overthe same connection with the client application 150 using the samenetwork communication protocol. GEM statements can be sent using abuilt-in SQL system procedure.

The index server 110 can include an authentication component 304 thatcan be invoked with a new connection with a client application 150 isestablished. Users can be authenticated either by the database system105 itself (login with user and password) or authentication can bedelegated to an external authentication provider. An authorizationmanager 306 can be invoked by other components of the database system150 to check whether the user has the required privileges to execute therequested operations.

Each statement can processed in the context of a transaction. Newsessions can be implicitly assigned to a new transaction. The indexserver 110 can include a transaction manager 344 that coordinatestransactions, controls transactional isolation, and keeps track ofrunning and closed transactions. When a transaction is committed orrolled back, the transaction manager 344 can inform the involved enginesabout this event so they can execute necessary actions. The transactionmanager 344 can provide various types of concurrency control and it cancooperate with a persistence layer 346 to achieve atomic and durabletransactions.

Incoming SQL requests from the client applications 150 can be e receivedby the SQL processor 312. Data manipulation statements can be executedby the SQL processor 312 itself. Other types of requests can bedelegated to the respective components. Data definition statements canbe dispatched to a metadata manager 306, transaction control statementscan be forwarded to the transaction manager 344, planning commands canbe routed to a planning engine 318, and task related commands canforwarded to a task manager 324 (which can be part of a larger taskframework) Incoming MDX requests can be delegated to the MDX processor322. Procedure calls can be forwarded to the procedure processor 314,which further dispatches the calls, for example to a calculation engine326, the GEM processor 316, a repository 300, or a DDI proxy 328.

The index server 110 can also include a planning engine 318 that allowsplanning applications, for instance for financial planning, to executebasic planning operations in the database layer. One such basicoperation is to create a new version of a data set as a copy of anexisting one while applying filters and transformations. For example,planning data for a new year can be created as a copy of the data fromthe previous year. Another example for a planning operation is thedisaggregation operation that distributes target values from higher tolower aggregation levels based on a distribution function.

The SQL processor 312 can include an enterprise performance management(EPM) runtime component 320 that can form part of a larger platformproviding an infrastructure for developing and running enterpriseperformance management applications on the database system 105. Whilethe planning engine 318 can provide basic planning operations, the EPMplatform provides a foundation for complete planning applications, basedon by application-specific planning models managed in the databasesystem 105.

The calculation engine 326 can provide a common infrastructure thatimplements various features such as SQLScript, MDX, GEM, tasks, andplanning operations. The SQLScript processor 312, the MDX processor 322,the planning engine 318, the task manager 324, and the GEM processor 316can translate the different programming languages, query languages, andmodels into a common representation that is optimized and executed bythe calculation engine 326. The calculation engine 326 can implementthose features using temporary results 340 which can be based, in part,on data within the relational stores 332.

Metadata can be accessed via the metadata manager component 308.Metadata, in this context, can comprise a variety of objects, such asdefinitions of relational tables, columns, views, indexes andprocedures. Metadata of all these types can be stored in one commondatabase catalog for all stores. The database catalog can be stored intables in a row store 336 forming part of a group of relational stores332. Other aspects of the database system 105 including, for example,support and multi-version concurrency control can also be used formetadata management. In distributed systems, central metadata is sharedacross servers and the metadata manager 308 can coordinate or otherwisemanage such sharing.

The relational stores 332 form the different data management componentsof the index server 110 and these relational stores can, for example,store data in main memory. The row store 336, a column store 338, and afederation component 334 are all relational data stores which canprovide access to data organized in relational tables. The column store338 can stores relational tables column-wise (i.e., in a column-orientedfashion, etc.). The column store 338 can also comprise text search andanalysis capabilities, support for spatial data, and operators andstorage for graph-structured data. With regard to graph-structured data,from an application viewpoint, the column store 338 could be viewed as anon-relational and schema-flexible in-memory data store forgraph-structured data. However, technically such a graph store is not aseparate physical data store. Instead it is built using the column store338, which can have a dedicated graph API.

The row store 336 can stores relational tables row-wise. When a table iscreated, the creator can specify whether it should be row orcolumn-based. Tables can be migrated between the two storage formats.While certain SQL extensions are only available for one kind of table(such as the “merge” command for column tables), standard SQL can beused on all tables. The index server 110 also provides functionality tocombine both kinds of tables in one statement (join, sub query, union).

The federation component 334 can be viewed as a virtual relational datastore. The federation component 334 can provide access to remote data inexternal data source system(s) 354 through virtual tables, which can beused in SQL queries in a fashion similar to normal tables.

The database system 105 can include an integration of a non-relationaldata store 342 into the index server 110. For example, thenon-relational data store 342 can have data represented as networks ofC++ objects, which can be persisted to disk. The non-relational datastore 342 can be used, for example, for optimization and planning tasksthat operate on large networks of data objects, for example in supplychain management. Unlike the row store 336 and the column store 338, thenon-relational data store 342 does not use relational tables; rather,objects can be directly stored in containers provided by the persistencelayer 346. Fixed size entry containers can be used to store objects ofone class. Persisted objects can be loaded via their persisted objectIDs, which can also be used to persist references between objects. Inaddition, access via in-memory indexes is supported. In that case, theobjects need to contain search keys. The in-memory search index iscreated on first access. The non-relational data store 342 can beintegrated with the transaction manager 344 to extends transactionmanagement with sub-transactions, and to also provide a differentlocking protocol and implementation of multi version concurrencycontrol.

An extended store is another relational store that can be used orotherwise form part of the database system 105. The extended store can,for example, be a disk-based column store optimized for managing verybig tables, which ones do not want to keep in memory (as with therelational stores 332). The extended store can run in an extended storeserver 125 separate from the index server 110. The index server 110 canuse the federation component 334 to send SQL statements to the extendedstore server 125.

The persistence layer 346 is responsible for durability and atomicity oftransactions. The persistence layer 346 can ensure that the databasesystem 105 is restored to the most recent committed state after arestart and that transactions are either completely executed orcompletely undone. To achieve this goal in an efficient way, thepersistence layer 346 can use a combination of write-ahead logs, undoand cleanup logs, shadow paging and savepoints. The persistence layer346 can provide interfaces for writing and reading persisted data and itcan also contain a logger component that manages a recovery log.Recovery log entries can be written in the persistence layer 352 (inrecovery log volumes 352) explicitly by using a log interface orimplicitly when using the virtual file abstraction. The recovery logvolumes 352 can include redo logs which specify database operations tobe replayed whereas data volume 350 contains undo logs which specifydatabase operations to be undone as well as cleanup logs of committedoperations which can be executed by a garbage collection process toreorganize the data area (e.g. free up space occupied by deleted dataetc.).

The persistence layer 346 stores data in persistent disk storage 348which, in turn, can include data volumes 350 and/or recovery log volumes352 that can be organized in pages which can form one or more pagechains. Different page sizes can be supported, for example, between 4 kand 16M. Data can be loaded from the disk storage 348 and stored to diskpage wise. For read and write access, pages can be loaded into a pagebuffer in memory. The page buffer need not have a minimum or maximumsize, rather, all free memory not used for other things can be used forthe page buffer. If the memory is needed elsewhere, least recently usedpages can be removed from the cache. If a modified page is chosen to beremoved, the page first needs to be persisted to disk storage 348. Whilethe pages and the page buffer are managed by the persistence layer 346,the in-memory stores (i.e., the relational stores 332) can access datawithin loaded pages.

The pages included in data volumes 350 can be configured to storeentries of variable sizes. Deleting entries in these variably sizedpages can result in fragmentation. A transient data structure can beused to store information about pages in the persistence layer 346 withfree space and deleted entries that can be reused.

Initially, after loading of a page into memory (one of the relationalstores 332), it is determined whether such page should be reorganized.Such determination can be based, for example, on whether the page isfragmented and/or how the page is configured. For example, if the pageis fragmented with entries of different sizes, the page can bereorganized causing a first portion of the page to be contiguouslyfilled with entries and a second portion of the page having free space.However, if the page is fragmented with entries having the same size,then such gaps in free space can be easily reused (i.e., the gaps can befilled thereby eventually filling all gaps). In some cases, the numberof entries with varying sizes needs to exceed a certain threshold tojustify the overhead required to reorganize the page.

After the page is reorganized or it is determined that it does not needto be reorganized, such page can be used. There can a phase in which thepage is virtually locked to check checksum, etc. and within this phaseonly the thread loading the page can access such page. This thread canalso handle any kind of reorganization, as no other thread can accessthe page in parallel.

FIG. 4 is a process flow diagram 400 in which, at 410, a page is loadedinto memory of an in-memory database system. Thereafter, at 420, it isdetermined whether to reorganized the page based on how such page isused. Based on this determination either, at 430, the page isreorganized by filling any free space gaps in memory if it is determinedto reorganize the page and use of the reorganized page is enabled, or,at 440, use of the page is enabled without reorganizing.

One or more aspects or features of the subject matter described hereincan be realized in digital electronic circuitry, integrated circuitry,specially designed application specific integrated circuits (ASICs),field programmable gate arrays (FPGAs) computer hardware, firmware,software, and/or combinations thereof. These various aspects or featurescan include implementation in one or more computer programs that areexecutable and/or interpretable on a programmable system including atleast one programmable processor, which can be special or generalpurpose, coupled to receive data and instructions from, and to transmitdata and instructions to, a storage system, at least one input device,and at least one output device. The programmable system or computingsystem may include clients and servers. A client and server aregenerally remote from each other and typically interact through acommunication network. The relationship of client and server arises byvirtue of computer programs running on the respective computers andhaving a client-server relationship to each other.

These computer programs, which can also be referred to as programs,software, software applications, applications, components, or code,include machine instructions for a programmable processor, and can beimplemented in a high-level procedural language, an object-orientedprogramming language, a functional programming language, a logicalprogramming language, and/or in assembly/machine language. As usedherein, the term “machine-readable medium” refers to any computerprogram product, apparatus and/or device, such as for example magneticdiscs, optical disks, memory, and Programmable Logic Devices (PLDs),used to provide machine instructions and/or data to a programmableprocessor, including a machine-readable medium that receives machineinstructions as a machine-readable signal. The term “machine-readablesignal” refers to any signal used to provide machine instructions and/ordata to a programmable processor. The machine-readable medium can storesuch machine instructions non-transitorily, such as for example as woulda non-transient solid-state memory or a magnetic hard drive or anyequivalent storage medium. The machine-readable medium can alternativelyor additionally store such machine instructions in a transient manner,such as for example as would a processor cache or other random accessmemory associated with one or more physical processor cores.

To provide for interaction with a user, the subject matter describedherein may be implemented on a computer having a display device (e.g., aCRT (cathode ray tube) or LCD (liquid crystal display) monitor) fordisplaying information to the user and a keyboard and a pointing device(e.g., a mouse or a trackball) and/or a touch screen by which the usermay provide input to the computer. Other kinds of devices may be used toprovide for interaction with a user as well; for example, feedbackprovided to the user may be any form of sensory feedback (e.g., visualfeedback, auditory feedback, or tactile feedback); and input from theuser may be received in any form, including acoustic, speech, or tactileinput.

In the descriptions above and in the claims, phrases such as “at leastone of” or “one or more of” may occur followed by a conjunctive list ofelements or features. The term “and/or” may also occur in a list of twoor more elements or features. Unless otherwise implicitly or explicitlycontradicted by the context in which it is used, such a phrase isintended to mean any of the listed elements or features individually orany of the recited elements or features in combination with any of theother recited elements or features. For example, the phrases “at leastone of A and B;” “one or more of A and B;” and “A and/or B” are eachintended to mean “A alone, B alone, or A and B together.” A similarinterpretation is also intended for lists including three or more items.For example, the phrases “at least one of A, B, and C;” “one or more ofA, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, Balone, C alone, A and B together, A and C together, B and C together, orA and B and C together.” In addition, use of the term “based on,” aboveand in the claims is intended to mean, “based at least in part on,” suchthat an unrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems,apparatus, methods, and/or articles depending on the desiredconfiguration. The implementations set forth in the foregoingdescription do not represent all implementations consistent with thesubject matter described herein. Instead, they are merely some examplesconsistent with aspects related to the described subject matter.Although a few variations have been described in detail above, othermodifications or additions are possible. In particular, further featuresand/or variations can be provided in addition to those set forth herein.For example, the implementations described above can be directed tovarious combinations and subcombinations of the disclosed featuresand/or combinations and subcombinations of several further featuresdisclosed above. In addition, the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. Other implementations may be within the scope of the followingclaims.

What is claimed is:
 1. A computer-implemented method comprising:loading, in an in-memory database system, a page into memory;determining whether to reorganized the page based on how such page isused; reorganizing the page by filling any free space gaps in memory ifit is determined to reorganize the page and enabling the reorganizedpage to be used; or enabling the page to be used without reorganization.2. The method of claim 1, wherein the determining comprises measuring anumber of different entry sizes used by the page.
 3. The method of claim1, wherein the determining comprises measuring an amount offragmentation within the page.
 4. The method of claim 3, wherein thedetermining is based on whether there are uniform entry sizes in thepage.
 5. The method of claim 3, wherein the determining is based onwhether the page is configured such that new entries are added andoldest entries are deleted when space is needed.
 6. The method of claim1 further comprising: storing information about the page in a transientdata structure in a persistence layer of the in-memory database systemidentifying free space within the page and deleted entries within thepage that can be reused.
 7. The method of claim 1, wherein the page isone of a plurality of pages forming a page chain.
 8. The method of claim7, wherein the page chain is encapsulated within a variable size entrydata container.
 9. The method of claim 1, wherein the reorganizingcauses the page to have a first portion with entries and a second,different portion, of contiguous free space.
 10. A system comprising: atleast one data processor; and memory storing instructions which, whenexecuted by the at least one data processor, results in operationscomprising: loading a page into memory; determining whether toreorganized the page based on how such page is used; reorganizing thepage by filling any free space gaps in memory if it is determined toreorganize the page and enabling the reorganized page to be used; orenabling the page to be used without reorganization.
 11. The system ofclaim 10 further comprising an in-memory database system that includesthe at least one data processor and the memory.
 12. The system of claim10, wherein the determining comprises measuring a number of differententry sizes used by the page.
 13. The system of claim 10, wherein thedetermining comprises measuring an amount of fragmentation within thepage.
 14. The system of claim 13, wherein the determining is based onwhether there are uniform entry sizes in the page.
 15. The system ofclaim 13, wherein the determining is based on whether the page isconfigured such that new entries are added and oldest entries aredeleted when space is needed.
 16. The system of claim 10, wherein theoperations further comprise: storing information about the page in atransient data structure in a persistence layer of the in-memorydatabase system identifying free space within the page and deletedentries within the page that can be reused.
 17. The system of claim 10,wherein the page is one of a plurality of pages forming a page chain.18. The system of claim 17, wherein the page chain is encapsulatedwithin a variable size entry data container.
 19. The system of claim 10,wherein the reorganizing causes the page to have a first portion withentries and a second, different portion, of contiguous free space.
 20. Anon-transitory computer program product storing instructions which, whenexecuted by at least one data processor forming part of at least onecomputing device, result in operations comprising: loading a page intomemory; determining whether to reorganized the page based on how suchpage is used; reorganizing the page by filling any free space gaps inmemory if it is determined to reorganize the page and enabling thereorganized page to be used; or enabling the page to be used withoutreorganization.